Too Low to Recover

An ice-induced stall sent a Phenom hurtling into houses near the approach end of the runway.

by Mark Lacagnina | September 6, 2016

According to the investigators, the warning signs were there. Airframe icing was imminent, and the airplane needed to be protected. But the warning signs were not heeded, and the protection was not provided. Moreover, the airspeeds used by the pilot during the final stages of the nonprecision approach were too slow for the existing conditions.

The subsequent ice-induced stall occurred at an altitude too low to permit recovery. The Embraer EMB-500 Phenom 100 descended out of control and struck three houses near the approach end of the runway at Montgomery County Airpark in Gaithersburg, Maryland, U.S. Three people in one of the houses were killed, as were the pilot and his two passengers. The airplane was destroyed by the impact and post-impact fire.

Close up of engine from EMB-520 accident in Gaithersburg, Maryland, December 2014.Image: U.S. National Transportation Safety BoardAerial view of EMB-520 accident in Gaithersburg, Maryland, December 2014.Image: U.S. National Transportation Safety Board

The accident occurred the morning of Dec. 8, 2014. The investigation by the U.S. National Transportation Safety Board (NTSB) concluded that the probable cause was “the pilot’s conduct of an approach in structural icing conditions without turning on the airplane’s wing and horizontal stabilizer deice system, leading to ice accumulation on those surfaces, and without using the appropriate landing performance speeds for the weather conditions and airplane weight.”

Based on the findings of the investigation, the NTSB called for the development of equipment for single-pilot jets that warns the pilots when the ice-protection systems should be activated. The safety board also recommended the development of training beyond what is currently required to pass a type rating check ride in such airplanes.

Slow Progress

The pilot, 66, was a physician and chief executive officer of a clinical research company. He held an airline transport pilot certificate and an EMB-500 type rating, which he had received about seven months before the accident.

The pilot had about 4,737 flight hours, including 136 hours in the EMB-500, 1,500 hours in Socata TBM-700s and 60 hours in an Aero Vodo­chody L-39C, a former Czech fighter-trainer.

The NTSB accident report noted that the pilot had been involved in a previous accident while landing a TBM-700 at Gaithersburg. That accident occurred on March 1, 2010, during an attempted go-around following loss of directional control after touchdown.1 The single-­turboprop climbed about 10 ft before descending in a left turn and striking trees. Damage was substantial, but the pilot, who was alone in the airplane, was not hurt. The NTSB concluded that the probable cause of the accident was “the pilot’s failure to maintain aircraft control while performing a go-around.”

After the 2010 accident, the pilot successfully completed a certificate re-examination by the U.S. Federal Aviation Administration (FAA) that comprised a one-hour oral examination and a one-hour flight examination that included instrument approaches, missed approaches and landings.

“FAA records also indicated that the pilot received an enforcement action for violating a temporary flight restriction on August 18, 2011,” the report said.

He had received training in the EMB-500 at two different facilities. “The company instructor who initially conducted the pilot’s transition training in the EMB-500 characterized the pilot as highly motivated, very intelligent and possessing a strong aptitude for memorization,” the report said.

“He stated, however, that the pilot had difficulty with planning and workload manage­ment, and sometimes became ‘task saturated,’ freezing up or fixating on a subtask at the expense of other critical subtasks. He said that, as a result, the pilot’s training progress was slow.”

‘Significant Weaknesses’

The pilot had requested an abbreviated transition training course in the EMB-500, but the instructor had convinced him that, based on his experience, a full course was required.

“However, after the pilot completed the [full] course, the instructor did not believe that he met the required standards to obtain a type rating in the EMB-500 and advised the pilot to receive more training,” the report said.

The pilot subsequently received 24 additional hours of flight instruction at another training facility before receiving his type rating.

“Although his instructors said that he was proficient by the time he passed his check ride and that all of the required special emphasis areas were addressed in some manner, evidence from the flight before the accident flight — as well as errors made by the pilot during the accident flight — revealed significant weaknesses in his capabilities,” the report said.

During the flight before the accident flight, data captured by the airplane’s cockpit voice and data recorder (CVDR) “showed that the pilot had problems managing altitude during arrival,” the report said. The airplane initially flew over the airport 5,400 ft above ground level (AGL), descended to 1,000 ft AGL on an extended straight-in approach and then climbed to 1,500 AGL before descending to the runway.

“The pilot also attempted to set flaps 2 on final without lowering the gear (which was out of sequence) and received a ‘landing gear’ aural warning as a result,” the report said.

The report also noted that the pilot’s records showed that he had flown the Phenom only about seven hours in each of the two months preceding the accident.

‘Bit of a Hurry’

The accident flight was intended to transport the pilot and two passengers from Horace Williams Airport in Chapel Hill, North Carolina, to Gaithersburg for a business meeting. That morning, the pilot called a line service facility at the Chapel Hill airport to advise that he would be departing at 0930 local time.

The line service technician who helped the pilot pull the Phenom from its hangar told investigators that the pilot “was ‘in a bit of a hurry’ but did not appear to be careless,” the report said.

However, other factors led investigators to conclude that “the pilot’s actions before takeoff for the accident flight were consistent with noncompliance with standard operating procedures.”

Elapsed time from start of the first engine to takeoff was six minutes, “which left the pilot little time to perform the procedures for the Power Up, Before Start, Engine Start (for the second engine) and After Engine Start checklists,” the report said.

CVDR data indicated that one item neglected on the Before Takeoff checklist was an airplane-configuration check. The CVDR did not record an aural annunciation of “takeoff OK,” which confirms that the flaps and pitch trim are set properly for takeoff, and the parking brake is not engaged. The annunciation is generated when the pilot presses the “T/O CONFIG” button on the center console.

Unheeded Warnings

The airplane departed from Chapel Hill at about 0945 local time. CVDR data indicated that the Phenom encountered instrument meteorological conditions about 15 minutes after takeoff.

The pilot manually activated the engine ­anti-ice system, which routes bleed air to the inlet cowls, and the wing and horizontal stabilizer deice system, which comprises pneumatic boots on the leading edges. The systems were deactivated about two minutes later and remained off for the duration of the flight.

The airplane was cruising at Flight Level (FL) 230 (approximately 23,000 ft) when the pilot received the Gaithersburg automated weather observing system (AWOS) broadcast, which indicated that surface winds were from 070 degrees at 2 kt, visibility was greater than 10 mi (16 km) and that there were a few clouds at 2,300 ft and an overcast ceiling at 2,800 ft. Temperature was minus 1 degree C (30 degrees F) and the dew point was minus 9 degrees C (16 degrees F).

The report said that the AWOS broadcast, as well as several pilot reports of structural icing, indicated that icing conditions could be expected during the descent and approach to Gaithersburg.

“Based on the AWOS-reported weather conditions, the pilot should have performed the Descent checklist items that appeared in the Normal Icing Conditions checklist, which included turning on the engine anti-ice and wing and horizontal stabilizer deice systems,” the report said. “That action, in turn, would require the pilot to use landing distance performance data that take into account the deice system’s activation.”

The performance data called for the use of a landing reference speed of 121 kt with the deice system activated and at the airplane’s landing weight.

“CVDR data show that, before beginning the descent, the pilot set the landing reference (Vref) speed at 92 knots, indicating that he used performance data for operation with the wing and horizontal stabilizer deice system turned off and an airplane landing weight less than the airplane’s actual weight,” the report said.

‘In and Out of Clouds’

The pilot began the descent from FL 230 at 1011. After establishing radio contact with Potomac Approach Control about 10 minutes later, he advised that he had the current weather observation at Gaithersburg.

The airport is uncontrolled and has a single, 4,202-ft (1,281-m) runway. It has one straight-in global positioning system (GPS) approach, a circling GPS approach and a VOR (VHF omnidirectional radio) approach.

The pilot requested, and received, clearance to conduct the straight-in GPS approach to Runway 14.

Because of a temperature inversion, the airplane encountered colder air during the descent. Total air temperature (TAT) was 12 degrees C (54 degrees F) above 6,000 ft but then decreased below 5 degrees C (41 degrees F).2 TAT remained below 5 degrees C for the duration of the flight.

Investigators determined that the airplane encountered icing conditions for at least 15 minutes during the descent and approach to Gaithersburg.

At 1031, the approach controller told the pilot to cross an intermediate fix 11.3 nm (20.9 km) from the runway at 3,000 ft and cleared him to conduct the GPS approach.

Shortly thereafter, a pilot on the ground at Gaithersburg used the common traffic advisory frequency (CTAF) to ask the pilot if there was “any precip out there.” The pilot replied, “We’re kind of in and out of the clouds here at three thousand.”

Loss of Control

Figure 1 — EMB-500 Airspeed Display

Notes: The top display shows stall-warning indications similar to what the accident pilot saw. The bottom display shows indications appropriate for icing conditions, which would have been presented if the ice-protection system had been activated.

Source: U.S. National Transportation Safety Board

The airplane was 5.5 nm (10.2 km) from the runway, with an indicated airspeed of 140 kt, when the pilot selected approach flaps. Airspeed subsequently began to slowly decrease.

The pilot told the right-seat passenger, “Your job is to find the airport. Just look straight ahead and say airport in sight.” Shortly thereafter, the passenger said “snow,” and the pilot replied, “Wow, there’s snow.”

At 1040, the passenger told the pilot that he had the airport in sight. The pilot confirmed the observation, selected full flaps and announced on the CTAF that the airplane was 3 nm (6 km) from the runway.

At this point, airspeed was decreasing below 115 kt as the autopilot increased pitch to maintain the GPS glide path. Airspeed had decreased to 92 kt at 1041:33 when the pilot increased power, which momentarily arrested the deceleration. However, as the pitch attitude and angle-of-attack (AOA) continued to increase, deceleration resumed.

“Because the deice system was not activated by the pilot before landing, the band indications (low speed awareness) on the airspeed display did not appropriately indicate the stall warning speed,” the report said.

“There would have been sufficient warning of an aerodynamic stall had the wing and horizontal stabilizer deice system been used during the approach.”

The report explained that when the wing and horizontal stabilizer deice system is activated, an aural stall warning is generated when AOA reaches 9.5 degrees, and the stick-pusher activates at 15.5 degrees. When the deice system is not selected, the stall warning horn sounds at an AOA of 21 degrees, and the stick-pusher activates at 28.4 degrees.

The Phenom’s AOA reached 9.5 degrees about 20 seconds before the pilot lost control of the airplane.

The airplane was still on autopilot at 840 ft (300 ft above field elevation) when it began to roll left and right. Airspeed was 88 kt and AOA was 21 degrees when the stall warning sounded and the autopilot disengaged at 1041:35. The aural stall warning continued, but there was no indication that the stick-pusher activated.

“Once the airplane stalled, its altitude was too low to recover,” the report said, noting that 300 to 500 ft of height typically is lost during a stall recovery in the Phenom.

Several large roll oscillations occurred before the airplane struck the three houses and the ground 900 ft (274 m) left of the extended centerline and about 4,000 ft (1,220 m) from the approach end of the runway at 1041:55.

Fire engulfed the airplane and one of the houses. The three occupants of the house on fire died of smoke inhalation; the pilot and his two passengers sustained multiple fatal impact injuries.

Awareness and Training

Based on the findings of the investigation, the NTSB recommended that the FAA and the General Aviation Manufacturers Association “work together to develop a system that can automatically alert pilots when the ice protection systems should be activated on turbofan airplanes that require a type rating and are certified for single-pilot operations and flight in icing conditions.”

“In a single-pilot operation, no additional crewmember is present to help detect an error of omission,” the report said. “Because pilots who may have neglected to activate the ice protection systems per procedures would receive a reminder of the need to do so, the NTSB believes that the benefit of active alerting to support the safe operation of this group of airplanes in icing conditions outweighs any potential drawbacks related to pilot overreliance on such prompting.”

Citing ongoing work by the National Business Aviation Association to improve the safety of very-light-jet operations, the NTSB recommended that the association lead an effort to develop “enhanced pilot training guidelines pertaining to risk management in winter weather operations, including the use of ice protection systems and adherence to checklist, with special emphasis given to deficiencies in pilot performance identified in this accident, and make the results of this effort available to the community of pilots who fly these airplanes.”

This article is based on U.S. National Transportation Safety Board Accident Report NTSB/AAR-16/01, “Aerodynamic Stall and Loss of Control During Approach, Embraer EMB-500, N100EQ, Gaithersburg, Maryland, December 8, 2014.” The report is available at <ntsb.gov>.

Notes

NTSB accident report ERA10CA155.

Total air temperature, also called stagnation temperature and free stream air temperature, is warmer than outside air temperature due to compression heating. TAT is shown on the pilot’s primary flight display in the EMB-500.